Constructivism is a learning theory that posits learners actively construct knowledge based on their experiences. Key theorists include Piaget, who described cognitive development in stages from childhood to adulthood, Vygotsky's zone of proximal development in which learning occurs with guidance, and Dewey's view of education as a social process centered on student-directed, hands-on learning. Implications for the classroom include analyzing students' levels, creating relevant activities, and using technology as a tool for research, assessment, and media in both teacher-guided and student-led learning.